The invention relates to an air-fuel control method and apparatus which detects the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine from the exhaust gas of the engine, and controls the air-fuel ratio of the mixture to a fixed value in response to the detection.
Conventionally, the output signal from a combustion components sensor was merely integrated. In a period of transient engine operation, during which the basic air-fuel ratio changed faster than the correcting speed of the integration control, the correction failed to follow the change of the basic air-fuel ratio. Further, when the combustion components sensor was inactive, feedback control of the air-fuel ratio was impossible, resulting in the generation of noxious exhaust gases.